1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio receivers used within such systems.
2. Description of Related Art
Communication systems are known to, support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, programmable gain amplifier, one or more intermediate frequency stages, a filtering stage, automatic gain control, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The programmable gain amplifier may further amplify the RF signals. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is further known, the signal strength of a received RF signal may vary dramatically (e.g., by 100 dB). The automatic gain control of the receiver functions to adjust the gain of the low noise amplifier, the programmable gain amplifier, and/or digital gain within the data recovery stage such that the receiver is sensitive enough to detect low power level signals and, once detected, to adjust the gain of these components to achieve nominal signal level. The automatic gain control also decreases the gain of the low noise amplifier, the programmable gain amplifier, and/or the digital gain of the data recovery stage when the received signal is a strong signal.
While such automatic gain control mechanisms work in many situations, there are some situations in which the automatic gain control does not adjust the gain of the low noise amplifier, the programmable gain amplifier, and/or the digital gain of the data recovery module. When this occurs, data is lost since the nominal signal level, which is expected for conversion to the digital domain, is not achieved.
Therefore, a need exists for a method and apparatus for automatic gain control of a radio receiver that overcomes the above mentioned limitations of existing automatic gain control circuits.